The present disclosure relates to a redundant control device and method, and more particularly, to a redundant control device and method of a high voltage direct current (HVDC) transmission system.
There are two power system interconnection methods, a typical one for interconnecting AC power systems as they are, and the other for interconnecting systems after converting AC power into DC power through a power converter. In recent, an interest in the method of interconnecting power systems after converting the AC power into the DC power is more increasing than the method of interconnecting AC power systems as they are. A high voltage direct current (HVDC) transmission system using a power converter is also installed between Jeju-island and Haenam-gun in Korea to interconnect power systems between Jeju-island and Haenam-gun.
An HVDC transmission method indicates a power supply method in which AC power generated at the power station is converted into DC power, and the DC power is transmitted and then re-converted into AC power in a power receiving region.
The DC transmission method has many advantages.
Firstly, since the size of a DC voltage is just about 70% of the maximum value of an AC voltage, the HVDC transmission system may easily perform device insulation and since its voltage is low, it is possible to reduce the number of insulators installed in each device and the height of an iron tower.
Since the DC method has less transmission loss than an AC method when the same power is transmitted, the best advantage of the HVDC transmission system is that power transmission efficiency may increase. The HDVC transmission system may transmit currents twice or more in the DC method than the AC method.
Since the HVDC transmission system may reduce wire consumption and the area of a transmission line, it is effective and also possible to enhance the stability of systems by connecting two systems having different voltages or frequencies.
The HVDC transmission system has no constraint on a power transmission distance and the DC transmission method needs inexpensive construction costs in land power transmission exceeding 450 Km or in submarine power transmission exceeding 40 Km as well.
Thus, the HVDC transmission system is used for a power system interconnection method of new renewable energy, especially for power transmission of a large offshore wind farm.
Since the distance between a power station and an electricity user in China and India is 1000 Km or longer, the prevalence of the HVDC transmission system is rapidly increasing recently.
Since a stable operation is very important to such an HVDC system, related facilities, such as a control of the HVDC have a redundant configuration.
Two systems that have a redundant configuration are typically connected through a SCSI cable, in which case a problem with disconnection or wiring occurs.
Also, there is a limitation in that a voltage for checking the operation of a counterpart system is affected by noise and thus a redundant control device malfunctions.